To become a professional cheese grader, Rory O'Brien had to take a series of tests. He already held a BA in Culinary Arts and had been working as a chef for years. In 2008, he was hired by Ornua, the Irish dairy group that markets Kerrygold butter and cheese to the world, and was asked to take a sensory analysis test to see if he had the palate to grade cheese.

"There were smell tests where you were given a bit of cotton wool in a test tube and had to pick up what it was," O'Brien said. "Things like lime zest, which are easy to identify when it's on a lime, are hard to pick up on cotton wool. But I could."

He also had to pass a written test and an exam where he was presented with a board of cheese and had to sort the flavors into mild, medium, mature, and other categories. "It turns out, I can taste," he said. "Which is just as well since I had been preparing food all that time."

From there, O'Brien took a cheesemaking course, and after much more schooling and several months of training with cheese graders, he became one of Kerrygold's professional cheese graders. That means he spends most of his time eating cheese in order to select which cheeses are good enough to be packaged and sold around the world under the Kerrygold name.

Kerrygold operates as a collective of Irish dairy co-operatives. Rather than using large scale agriculture, all of the milk that makes Kerrygold's cheese and butter comes from relatively small farms scattered around the country. These farms have, on average, 75 cows apiece, and they graze on grasslands for the majority of the year. Grassfed milk isn't just a marketing term. Cheese and butter that comes from the milk of grassfed cows has certain properties that contribute to the color and taste of those dairy products, particularly fatty acids and beta carotene, which is why grassfed butter is often yellower in appearance and softer in texture than butter from cows fed with mixed rations.

From the family farms, the dairy gets manufactured into cheese at various locations around the country. One of the largest facilities is Kerrygold Park in Cork, in the South of Ireland, where the majority of butter production takes place. Cheese aging isn't as concentrated into one facility, which means that O'Brien's job involves a great deal of travel.

O'Brien and the other graders use a tool called a cheese iron—a long, hollow tube with a handle—to extract samples from the center of a 20-kilogram block. From the taste and texture of the cheese, they determine which blocks will be set aside to age more, and which are of lower quality and should be funneled into things like processed cheese.

"We're looking for the amount of pressure from the cheese, how firm it is," O'Brien said. "We smell it and judge the aroma. We look for any defects, any cracks, anything that doesn't look right."

They also look for different signals depending on the cheese type. For example, in Kerrygold's Skellig cheese, a cheddar that's aged up to two years and has a caremlized sweetness to it, O'Brien will also check for the formation of calcium lactate crystals, those tiny white spots you might notice in aged Cheddar or harder cheese like Pecorino Romano and Grana Padano. Those crystals are intentional, as is the slightly drier, crumblier texture of those cheeses.

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The other cheeses in Kerrygold's lineup have different characteristics that O'Brien and the graders look for. The Blarney Castle Gouda-Style cheese is milkier and milder. "Nice on a burger and not a million miles away from monterey jack," he said. The aged and reserve cheddars that Kerrygold sells have increasing levels of sharpness, and a kind of savory mouthfeel. The higher acid level in the cheese is literally mouthwatering—it stimulates saliva production. Their Dubliner cheese, developed for the German market, is found in the cheddar section but is actually a cross between cheddar, parmesan, and Emmenthal cheese.

At their tastings, the graders start with the mildest cheeses and work their way up to the more flavorful, mature cheeses. They chew and spit out the samples—the amount of cheese they grade every day makes eating it all but impossbile. They cleanse their palates with fizzy water in between bites. "With the more mature cheese, your palate just gets exhausted," O'Brien said.

The variations between cheeses made with the same exact same recipe and cultures is astounding. "It's amazing how much diversity there is in cheese [...] and there's an awful lot of work that goes into it," O'Brien said. The offerings evolve depending on hundreds of tiny variables, from age to temperature to location in the warehouse. "Cheese is a living product," O'Brien said. Think about that the next time you're digging into a cheese board.